Method for the production of quality cotton yarns involving a low-cost process, free of environmental pollution

ABSTRACT

A method for cotton purification is described, where the cotton is subject to a purification process in water. The process solution contains calcium hydroxide and a non-ionic detergent wetting agent. Following this processing the cotton is rendered hydrophilic. The cotton is carried in a net with simultaneous removal of the adsorbed processing solution. It is then washed and bleached with H 2  O 2  or ClONa in a two-stage process. The effluent water is processed by anaerobic digestion in the thermophilic region for the production of biogas. The effluent water from the anaerobic digestion process is further processed by aerobic biological treatment. The whole process operates with energy self-sufficiency without resulting in environment pollution. Finally, a high purity cotton is produced with high water absorptivity which is suitable for spinning for the production of quality cotton yarns suitable for weaving quality fabrics or dyeing.

This application is a 371 of PCT/GR95/00015 filed Sep. 5, 1995.

This invention refers to an original method for the processing of cottonyarns: By this method, the traditional mechanical spinning process issubstituted by a wet process which involves complete purification of thecotton by rendering it hydrophilic. This process is self-sufficient interms of energy consumption and does not lead to environmentalpollution.

The textiles industry is a field of technical and industrial activitysince the Renaissance period. The first industrial installations andspecialised industrial equipment have been developed for textilesprocessing. The textiles industry consumes mainly cotton, which is notbeing produced in Central Europe, where industrial equipment andinstallations were first developed. Hence, large capital intensivedevelopments were necessary in the cotton-producing countries for theexploitation of the said raw material. Greece is among the cottonproducers, indeed the major European producer. Among the European Unioncountries, Greece is the country most depending on the cotton and yarnmanufacturing industry, an industry requiring highly expensiveindustrial installations, often becoming problematic and economicallyunsound. With a production of 700,000 tons/year the problems in theindustrial exploitation of this industrial agricultural product mayreflect badly on the overall economic performance of the Country.

The exploitation of cotton for yarn production is developed along thefollowing series of processes:

a) Mechanical purification and arrangement of yarns, where in more than10 different equipment of a high capital and operating cost are used.

b) Chemical purification by mercerising and scouring, where highlyexpensive installations are used, and where an alkaline effluent,difficult to handle, is released.

c) Yarn dyeing, where large volumes of water are consumed, and wherecoloured effluents are released.

Thus, the cotton yarn production and the cotton fabric productioninvolve complex processes involving high production costs, a highconsumption of water and the release of toxic and other harmfulpollutants.

The inventor has been intensively involved in Research and Developmentwork aiming at the reduction of production costs and of waterconsumption and at the elimination of environmental pollution, for thereduction of the overall cost of yarn and fabric production from cotton.

It was observed that the utilization of devices for cotton accommodationby lap and yarn formation is not possible, as wet processes follow theyarn production process.

It was also observed that cotton can be directly introduced into a wetprocess, as its presence in an aqueous environment will induce fibreorientation. Should this be combined with cotton purification byrendering it hydrophilic to some desirable extent, the process will becomplete and cotton will assume a form convenient for spinning, whichwill not be prone to agglomeration.

It was also observed that this production process leads to yarn andfabric production at a reduced cost, involving a smaller waterconsumption and the elimination of environmental pollution problems.This production process will also lead to higher quality--lower coastcotton yarn and fabrics.

This invention refers to and describes a method for yarn and fabricproduction featuring the above advantages leading to cotton yarnproduction (and subsequently cotton fabric production) in an overallproduction process free of environmental pollution, which involvesgeneration of heat in the form of biogas produced by the anaerobicdigestion in the thermophilic region of the waste material and refuseproduced. Thus, this production process constitutes a clean productiontechnology which is self-sufficient in terms of its energy requirements.

According to this invention, the cotton which is received in packages ispassed to a tank filled with water containing calcium hydroxide at aratio of 2-4% by weight of cotton. It also contains non-ionic detergentat a quantity of 2-5 gr./liter of process water. The cotton is suspendedin excess water in the order 1-10 or 1-20 weight/volume. The cotton iscarried in a polypropylene net and heated to a temperature of 60° to150° C., (preferably 60°-80° C.) with raw heating steam and beingcontinuously agitated for a time period of 1-3 hours. Following itsheating, it is lifted by a crane and is carried to a unit comprising ofa series of horizontal presses where it is compressed to 20 atm. withsimultaneous water removal. The compressed cotton is washed in waterwhich originates from the decoloration unit downstream and is thenconveyed to the decoloration unit, where it is bleached in the presenceof 10% ClONa, or 10% hydrogen peroxide or 5% ozone solution. Following atwo-stage processing, the cotton is received at a high degree ofwhiteness, in the order of 85-90 degrees lovipont. The effluent waterfrom the bleaching process is used for washing the cotton in thepresses.

Thus a high purity cotton of 80-90 degrees lovipont and of controlledhydrophilic properties (absorptivity of 5-20 gr. water/gr. cotton) isproduced, featuring a water absorption rate of 0.5-1.5 gr. water/gr.cotton/minute. The hydrophilic nature of the final product depends onthe duration and conditions of processing with calcium and detergent.The results of this process are summarised in Tables 1 and 2.

                  TABLE 1                                                         ______________________________________                                        Processing Conditions                                                         Ca (OH) 2   Levapon      Temperature                                                                             Time                                       gr./%       gr./lit      °C.                                                                              mins                                       ______________________________________                                        1      0.00     0.4          75      120                                      2      0.00     3.8          75      120                                      3      4.00     0.4          75      120                                      4      4.00     0.8          75      120                                      5      4.00     1.1          75      120                                      6      4.00     1.6          75      120                                      7      4.00     2.5          75      120                                      8      4.00     3.8          75      120                                      9      4.00     0.4          60      120                                      10     4.00     2.5          60      120                                      11     4.00     2.5          60      360                                      12     4.00     0.4          75      360                                      13     4.00     3.8          75      360                                      14     4.00     0.4          135     360                                      15     4.00     3.8          135     360                                      16     2.00     2.1          60      240                                      17     2.00     2.1          105     240                                      18     2.00     2.1          105     240                                      19     2.00     2.1          75      240                                      20     2.00     2.1          105     120                                      ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Results                                                                       Hydrophilic        Absorption                                                                              Yield                                            properties         Ratio     %                                                ______________________________________                                        1      6.53            0.02      99.3                                         2      8.10            0.20      86.4                                         3      10.48           0.55      87.8                                         4      13.5            0.6       86.6                                         5      15.5            0.72      85.8                                         6      17.5            0.81      85.2                                         7      19.5            0.9       84.8                                         8      17.32           0.94      85.2                                         9      13.20           1.08      87.3                                         10     18.14           1.12      84.2                                         11     16.31           1.29      83.3                                         12     11.26           0.7       85.5                                         13     12.00           1.8       84.8                                         14     10.05           0.71      85.7                                         15     17.84           1.71      83.7                                         16     17.20           1.45      87.4                                         17     17.99           0.96      86.8                                         19     17.53           0.91      87.1                                         19     17.28           0.98      86.3                                         20     17.84           0.91      84.11                                        ______________________________________                                    

From the results of the above Tables it is shown that the principalparameters of cotton purification and of rendering the materialhydrophilic is the quantities of detergent and calcium hydroxide added.Raising the temperature has a small effect on the technologicalcharacteristics of the product and leads to a decrease of the yield. Thedetergent particularly, is of a non ionic nature (Levapon was found tobe the most suitable material as it has a high activity). Calciumaddition is also important. Optimum conditions hence are: a temperaturein the order of 60°-80° C., a ratio of cotton to process water in theorder of 1/15 to 1/20, an addition of calcium hydroxide at a ratio of2-4% w/w and of Levapon at a ratio of 0.2-4 gr./lt. of process solution.

Then, the cotton is dried by conventional methods, i.e. in drying towerswith rising hot air, whereas the cotton is mercerised to the desireddegree of purification. It is then subject to spinning processesresulting in higher quality yarns for dyeing or weaving.

The process and cleaning water streams which carry chemicals and heat,as well as the resulting solid waste stream, are continuously recycledwith a substitution of 10-20% of the quantity of the process water. Thewaste stream removed has a constant BOD load of 20,000-40,000 and COD of50,000-100,000. It is passed to the installations for anaerobicdigestion which operate in the thermophilic region in a BIOMET PROCESSunit (invented and demonstrated by the inventor) with a yield in biogas(containing methane in the order of 85%) of 0.5 cu.meters/kg of organicmatter degraded. The effluent water produced, following the anaerobicdigestion, can be used as process water and is finally subject toaerobic biological treatment to effluent water of BOD 100.

The above method constitutes an original approach towards cottonprocessing for yarn production, introducing an innovation both in termsof the process used and of the results obtained. It offers innovativeoperation, it constitutes a clean technology and it operates with energyself-sufficiency without causing environmental pollution.

In general the invention introduces maximum economy in the processing ofcotton for yarn production, reducing the cost of installations, as thecotton can be sorted in terms of quality and length of fibre and as itwill be subject to a simple treatment which will not lead to thereduction of the strength of the cellulosic mass. The cotton will bedelivered at an advanced degree of processing Finally, followingtreatment by the method proposed by this invention, high quality yarnswill be produced, as the cotton will have been purified and renderedhydrophilic, according to the exploitation requirements. This processresults in a high quality product and substitutes the mercerisingprocess. All these quality and economy--related features are combinedwith the need for simple and low-cost installations operating free ofenvironmental pollution.

EXAMPLE NO 1

10 kg of cotton carried in a polypropylene net are brought into a 1cu.m. capacity tank containing 200 lt. of water, 0.4 kg calciumhydroxide and 2.5 gr./lt. Levapon. The contents of the tank are heatedto a temperature of 75° C. Heating with continuous agitation of cottonlasts for three hours. Then, the net is lifted by a crane and passed toa horizontal press where it is compressed by the application of apressure of 20 atm. with simultaneous water removal. The resultingcotton product contains moisture at 20%. It is then washed with waterfrom the bleaching process and then transferred, always in the net, to adecolorisation unit containing a 20% H₂ O₂ or a 20% ClONa solution. Itis then subject to two-stage bleaching at installations similar to thosefor bleaching paper-pulp. Finally, a degree of bleaching (whitening) of86 degrees lovipont is achieved with a yield of 86.4%. The product didnot show any difference in its mechanical properties, it has hydrophilicproperties expressed as absoptivity of 17.10 gr. water/gr. cotton and arate of water absorption of 0.81 gr. water/gr. cotton/minute.

The process water was recycled by substituting 20% of it by freshprocessing solution. The pollutant load was stabilised at 22,000 BOD and48,000 COD. Thus, the steady state consumption of chemicals can bereduced to 20% of the chemicals originally present in the tank per unitcotton produced, i.e. 0.8 kg calcium hydroxide/100 kg cotton and 0.5 gr.detergent/lt. water.

EXAMPLE No 2

10 kg of cotton carried in a polypropylene net are brought into a tankcontaining 150 lt. of water, calcium hydroxide at a ratio of 2% byweight of cotton and 2.1 gr. of Levapon/liter of solution. The contentsof the tank are heated by raw steam to a temperature of 60° C. for threehours. The material is then compressed and bleached as in Example No 1.The product did not show any difference in its mechanical properties, ithas hydrophilic properties expressed as an absortivity of 18.280 gr.water/gr. cotton and a rate of water absorption of 0.98 gr. water/gr.cotton/minute. The process water was recycled by substituting 20% of itby fresh processing solution. Thus, actual chemicals consumption is 0.4kg calcium hydroxide/100 kg cotton and 0.41 gr. Levapon/lt. water.

EXAMPLE No 3

In an enclosure of a capacity of 1 cubic meters 20 kg of cotton in apolypropylene net and 300 lit. of water containing 0.8 kg calciumhydroxide and 2.5 gr. Levapon/liter are placed. The total enclosure isheated at 135° C. for two hours. The cotton is removed and compressed ina horizontal press by the exertion of a pressure of 20 atm., reaching amoisture content of 20%. It is then washed and bleached in a two-stageprocess as per the Examples No 1 and 2. The following product is finallycollected:

Experiment a:

Yield 85.7%; hydrophilic properties expressed as an absorptivity of15.04 gr. water/gr. cotton; rate of water absorption 0.71 gr. water/gr.cotton/minute

Experiment b:

Yield 85.2%; hydrophilic properties expressed as an absortivity of 15.82gr. water/gr. cotton; rate of water absorption 0.82 gr. water/gr.cotton/minute

The process water was recycled by substituting 20% of it by freshprocessing solution. Thus, actual chemicals consumption is 0.8 kgcalcium hydroxide/100 kg cotton and 0.5 gr. Levapon/lt. water.

EXAMPLE No 4

In an enclosure of a capacity of 0.5 cubic meter, 15 kg of cotton in apolypropylene net and 300 lit. water containing 0.3 kg calcium hydroxideand 2.1 gr. Levapon/liter are placed. The total enclosure is heated at105° C. for four hours. Following the cleaning and bleaching processesexplained in examples 1-3, the cotton is received at a yield of 86.8%and has the following properties: hydrophilic properties expressed as anabsortivity of 17.99 gr. water/gr. cotton; rate of water absorption 0.96gr. water/gr. cotton/minute

EXAMPLE No 5

The effluent water replaced by fresh processing solution has anenvironmental load of 30,000 BOD and 50,000 COD. It is fed to aninstallation of anaerobic digestion, operating in the thermophilicregion and producing 0.47 kg of biogas (containing 85% methane)/CODreduced. This is equivalent to a degree of pollution reduction of85-88%. Part of the effluent water stream from the anaerobic digestiontreatment is recycled into the process water, the rest being furtherprocessed at aerobic biological treatment installations for theproduction of water stream of BOD 100 which can be safely rejected tothe environment.

The biogas produced is used for the production of the steam used for theprocessing of cotton. Indeed, in the same as for the process water whichis recycled to a degree of 60-80%, the energy requirements for heatingthe cotton are also reduced. 60-70% of the biogas produced can be usedfor electricity generation for the needs of the plant. This will dependon the size and the design of the plant.

I claim:
 1. A method for spinning cotton, comprising the stepsof:passing cotton into a processing solution of calcium hydroxide whichis at a concentration of 2-4% by weight of calcium to cotton, and anon-ionic detergent which is at a concentration of 0.4-4 grams/liter,wherein the concentration of cotton in the solution is 10-20 volumes ofwater per weight of cotton, heating the solution with agitation at atemperature of 60° to 150° C., for 1-3 hours, transporting the cotton toa press, removing water from the cotton by pressure, bleaching thecotton in the presence of a solution of 10% ClONa or 10% hydrogenperoxide, washing the cotton in water, drying the cotton, and spinningthe cotton that is produced into a yarn.
 2. The method of claim 1,whereby the produced cotton has a water absorptivity of 5-20 gramswater/gram cotton.
 3. The method of claim 1, wherein the produced cottonhas a water absorption rate of 0.3-1.4 gram water/gram cotton/minute. 4.The method of claim 1, wherein 20-40% of the original processingsolution is substituted with recycled fresh solution.
 5. The method ofclaim 4, wherein the substituted solution is anaerobically digested, anda biogas is released at a rate of 0.45-5 kg/kg COD reduced.
 6. Themethod of claim 1, wherein the cotton is enclosed in a polypropylenenet.
 7. The method of claim 1, wherein said pressure to remove water is20 atm.
 8. The method of claim 1, wherein said temperature is 60°-80° C.9. The method of claim 1, wherein the cotton after the washing step hasa lovipont grade of 85-90.
 10. A cotton product produced by the methodof claim 1, which has a water absorptivity of 5-20 grams water/gramcotton.
 11. A cotton product produced by the method of claim 1, whichhas a water absorption rate of 0.3 to 1.4 gram water/gram cotton/minute.